Re: [Tinycc-devel] tcc fails UBSan and ASan

[Michael Matz]

Hi,

On Sat, 26 Jan 2019, Giovanni Mascellani wrote:

> This already prints lots of errors when tcc compiles libtcc1.a, mostly
> about unaligned struct access. An example:
>
> > tcctools.c:189:21: runtime error: member access within misaligned address 
> > 0x564f628c4d3c for type 'struct Elf64_Shdr', which requires 8 byte alignment
> > 0x564f628c4d3c: note: pointer points here
> >   00 00 00 00 01 00 00 00  01 00 00 00 06 00 00 00  00 00 00 00 00 00 00 00  00 
> > 00 00 00 40 00 00 00
> >               ^

Uninteresting problem.  TCC supports only architectures where 
non-naturally aligned accesses are fine (or at least 4-byte aligned 
accesses).

> > tcctest.c: In function ‘switch_test’:
> > tcctest.c:1969:6: error: case label does not reduce to an integer constant
> >       case 4LL << 61:
> >       ^~~~

That's tcctest.c.  It intentionally contains several non-standard 
constructs.

> Some use-after-free are found in 07_function, 25_quicksort,
> 26_character_constants and 80_flexarray.

Also testcases.  They shouldn't be changed to cater for such checking (or 
if, then only carefully so, so that they afterwards indeed still test what 
they were supposed to).

> I can try to fix them, but maybe people more knowledgable than me might
> be quicker and produce a more correct fix.

If you can fix the misaligned accesses without using memcpy or similar 
100% portable means that just busily change code to please automatic 
tools then fine.  Please don't change the testcases for automatic tools.


Ciao,
Michael.